An AOT-COT Dual-Mode Three-Level Buck Converter With Wide Load and Input Ranges

This paper presents a dual operation mode wide input-range three-level buck dc-dc converter. The converter can operate in either continuous-conduction mode (CCM) with a constant-frequency adaptive-on-time ($\mathrm{CF}-\mathrm{AOT}$) control or in discontinuous-conduction mode (DCM) with a constant-on-time (COT) control, depending on the load condition in order to achieve high power conversion efficiency over a wide load range. A clock-free scheme is proposed to generate a duty signal with a 180° phase shift without using a clock, thereby enabling the converter to achieve a fast load response when a load current step occurs. A DCM zero-voltage-switching (ZVS) control scheme for the low-side power transistors during off-time is also developed to remove the switching power loss due to V-I overlap, thereby improving the efficiency in light load condition. Simulated in a 180 nm BCD process, the proposed converter regulates the output voltage at 1 V and achieves a maximum power efficiency of 89.6% in CCM and 85% in DCM. Besides, the proposed converter shows a fast load transient response with a $29-\mathrm{mV}$ output voltage droop for a 2 A current step with 10-ns rising time.